Supervisory alarm system



Oct. 13, 1953 v. T. CALLAHAN ET AL 5 SUPERVISORY ALARM SYSTEM Filed Aug. 14, 1952 3 Sheets-Sheet l FIG.

L 7. CALLAHAN m/vavrops L 0' Ki a-W ArTOR/VEV Oct. 13, 1953 v. T. CALLAHAN ET AL 5 SUPERVISORY ALARM SYSTEM Filed Aug. 14, 1952 3 Sheets-Sheet 2 FIG. 2

Z' CALLAHAN D. FRY

gig W A 770 R/VEY I Oct. 13, 1953 v. T. CALLAHAN ETAL 2,655,646

SUPERVISORY ALARM SYSTEM 3 Sheets-Sheet 3 7 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I kiwhwq INDY I I I I I l/ 7.' CALLAHAN L. DF/PV 8 Eu m n .L mx 8 8b In \EB J R 56 /NVE/VTO/P$ ATTORNEY WW m at Nub Patented Oct. 13, 1953 SUPERVISORY ALARM SYSTEM Vincent T. Callahan, Englewood, and Lloyd D.

Fry, Chatham, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 14, 1952, Serial No. 304,317

Claims. "5

This invention relates to power supply apparatus and particularly to such apparatus for supplying current to a load from two engine-driven generators during alternate time periods.

In a specific embodiment of the invention herein shown and described for the purpose of 'illus tration, there are provided two engine-driven generator sets for alternately supplying current to a load. When a first of the generators, for example, has been supplying current to the load for a predetermined period, a motor-driven cam switch closes a first circuit for controlling the starting of the engine for driving the generator of the second engine-driven generator set. If the second engine-driven generator starts, the first generator continues to supply current to the load during a period in which the output voltage of the second generator build up. When the output voltage of the second generator has increased to a predetermined value, relay means are energized for controlling the energization of a transfer switch, after a delay period, and the transfer switch operates to transfer the load from the first generator to the second generator. If the output voltage of the second generator remains at a sufficiently high value when the load is transferred to the second generator, means are provided for shutting down the first enginedriven generator.

When the second generator has been supplying a current to the load for a predetermined time period, the cam switch closes a second circuit for controlling the starting of the first en 'gine-driven generator, the first circuit having previously been opened by the cam switch. When the output voltage of the first generator reaches a certain operating value, the transfer switch is again operated, after a delay period, and the load is transferred from the second generator to the first generator. Subsequently the second engine-driven generator is shut down.

Under certain abnormal operating conditions, a generator which is supplying current to the load may be shut down prior to the expiration of its normal operating period. In this case the second engine-driven generator is started and, when its output voltage reaches an operating value, the transfer switch is operated with a minimum delay to transfer the load to the second generator. In order to restart the first generator after the cause of its failure has been corrected, it is necessary toreset certain relays manually. If, after one of the engine-driven generators has been started and the load has been transferred to it, the generator output voltage should drop below a predetermined value, means are provided for preventing the stopping of the second engine-driven generator and the load is transferred back to the second generator.

Each of the engine-driven generator sets which alternately supply current to the load is provided with motor operated air recirculating louvers, the motor and its controller being connected across the load through fuses. Relay means are provided for operating an alarm when one of the fuses blows and for blocking the operation of the alarm in response to failure of load voltage while one of the generators is operating to produce an output voltage. However, there is provided a second alarm which is operated in response to load voltage failure. Relay means are also provided for causing the operation of the first mentioned alarm in the event that both generators fail to produce output voltage, the second alarm also being operated for this condition due to failure of voltage across the load.

Figs. 1, 2 and 3, when placed with respect to each other as shown in the diagram of Fig. 4, are a schematic view of a power supply apparatus embodying the invention.

Referring to the drawing there are provided for supplying alternating current to a load l6 during alternate time periods two similar diesel engine-driven, single phase alternators. One of the alternators I0 driven by a diesel engine H and control apparatu therefor are shown within the dash line enclosure M. The apparatus included Within a box [5 is the same as that provided within the enclosure I4, and includes the second alternator l2 driven by a diesel engine I 3. The apparatus is designed so that one of the engines will run for a desired period, say twelve hours, and then the other engine will run for a desired period of say twelve hours, etc.

Oneof the output terminals of each of the alternators l0 and I 2, and one of the load terminals are connected to ground. The remaining output terminals of the alternators, respectively, are connected to the load [6 through contacts of a transfer switch TS. With the switch TS in the position shown in the drawing, output terminal ll of alternator i0 is connected by way of TI through armature I of transfer switch TS to line Ll going to terminal 2| of load 16. Output terminal 18 of alternator I0 is connected by way of line T2 through armature 2 of transfer switch TS to line L2 going to a terminal 22 of load 16. When transfer switch TS is energized, output terminal I9 of alternator I2 is connected by Way of lead 2T! through armature l of transfer switch TS to line Ll going to load terminal 2| and output terminal of alternator I2 is connected by way of lead 2T2 to armature 2 of transfer switch TS to line L2 going to load terminal 22. The switch TS is of the type in which a shaft carrying the switch armatures I, 2, 3 and 4 is rotated alternately in opposite directions in response to successive pulses of energy supplied to the electromagnet of the switch. Therefore, when the switch TS is subsequently again energized the switch armatures l, 2, 3 and 4 will be moved back to the position shown in the drawing to reconnect the load to alternator l0.

There is provided a cycle timer CT comprising a motor 23 for driving the cams 24 and at a rate such that the cams make a complete revolution in twenty-four hours, for example, contacts 2 end 3 of the cycle timer CT being closed alternately. One terminal of motor 23 is grounded and the other terminal is connected to lead LIF- and thence through a fuse 56 to line Ll going to load terminal 2|, thereby energizing the motor.

The apparatus and its operation will be further described assuming that diesel engine 2 l is about to complete twelve hours of operation. It should be noted that contact 6 of cycle timer CT opened about one-half hour after the starting of engine H and that relay lCL remained energized, after the opening of contact 4 of CT, by current supplied over a circuit from line Ll, line LIE, contact h"; of relay ZCL, contact 3 of relay ICL, winding of ICL, line LZF, fuse 54 to line L2, LI and L2 being connected to load terminals 2! and 22, respectively. When contact 2 of the timer CT closes, relcy 2CL is energized due to the completion of a. circuit traced from line Ll through line LlF, contact 2 of timer CT, the winding of relay 20L and line L21 to line L2. Contact ill of relay 2CL opens due to the operation of relay 2CL to cause relay [Oh to release, and contact 3 of relay 2CL closes to lock up relay 2CL. The release of relay ICL completes a circuit from output terminal IQ of alternator [2 through lead 2Tl, reactor 2'1, condenser 28, rheostat 29, winding of power failure relay ZPF, contact 9 of relay ICL and lead 2T2 to output terminal 20 of generator l2, thereby completing an energizing circuit for relay ZPF when alternator I2 is driven by the engine 13. Operation of relay ZCL opens its contact 9 to open a circuit comprising line T2, cont: ct 9 of relay 20L, winding of power failure relay iPF, rheostat 30, condenser 3| and reactor 32 to line Tl, thereby releasing relay IPF. Release of relay lPF opens at its contact the circuit from line T2 through contact 9 of relay 2CL, the contact of relay lPF, the contact 3 and the winding of transfer relay [TR to line Tl, thereby releasing reley ITR.

Four circuits are afiected by the release of relay lTR. Contact 3 of relay [TR opens to remove the lock-up path for that relay. Contact 9 of relay ITR closes to prepare a circuit for transfer switch TS so that it will operate when transfer switch control relay 2TSC operates at the end of the operation of the hold-over timer IHOT, contact l and the Warm-up timer ZWUT, contact 8. The energizing circuit for transfer switch TS may be traced from line 2T1, contact 9 of relay ITR, the contact of relay 2TSC, armalnire 4 of transfer switch TS, the winding of switch TS and armature 3 of switch TS to line 2T2. Contact. 1-0 of relay lTR, closes and prepares the circuit to hold-over timer 2HOT when engine. 13 is operating and engine H is warming up for the next operating period. Contact ll of relay iTR closes to complete a circuit from negative battery through fuse 35, contact ll of relay ITR, winding of main control relay 2MC, contact 8 of over-crankin relay 20C, contact 5 of low oil pressure and high water temperature relay ZLOHW, contact k of. over-speed trip relay 2OS, lead PX2 to apparatus 15 and overload timer OLT to ground, thereby operating relay 2MC.

With the main control relay 2MC operated, contact 5 thereof opens so that relay I'I'R will not operate immediately upon return of power from generator l0. Contact 3 of relay 2MC closes to complete a circuit from ground through contact 3 of relay 2MC, winding of pilot relay 2P, contact ll of relay ITR and fuse 36 to negative battery, thereby operating relay 2P. Contact l of relay 2MC closes to complete a circuit from negative battery, through fuse 36, contact I of 2MC, lead Pl of apparatus 15 and relay PI to ground, thereby operating relay PI of apparatus l5 which is the control relay for the engine air shut-down circuit.

The operation of pilot relay 2P affects two circuits. Contacts 3 of relay 2? close to complete a circuit from negative battery through contacts 3 of relay 2P, lead THS to apparatus l5, winding of relay ASDI and contact of thermal relay ASDT of apparatus l5 to ground. Relay ASDI operates and locks up through its contact 3. Operation of relay ASDI prepares, through its contact 8, an energizing circuit for operating the air shut-down valve ASD for engine l3 if relay PI releases because of intentional shutdown or trouble shutdown. Contacts 2 of relay 2P close to apply negative battery through contact 4 of relay 20C, contact 2 of relay 2?, contact 6 of relay 2AP, lead CO4 going to apparatus l5, contact of cranking cut-out relay CCO, emergency switch ESW and winding of starting contactor ST to ground, thereby operating the starting contactor ST. Operation of contactor ST completes a circuit for operating starting motor M for cranking the diesel engine l3. After the engine fires and reaches a speed of seven hundred to eighth hundred revolutions per minute, the contacts of cranking cut-out switch CC5 close to cause the cranking cut-out relay 000- to operate, thereby opening the energizing circuit for starting relay ST causing it to release. The relay CCO is operated all of the time that the engine is running.

After engine l3 has started and is drivin the alternator I2, engine H continues to drive alternator ID for a subsequent period and the output of alternator l9 continues to supply current to the load. When the output voltage of alternator l2 builds up to about 94 per cent of normal voltage, power failure relay 2PF and alternator potential relay ZAP are energized by way of leads 2Tl and 2T2 to cause the operation of these relays. Operation of relay 2AP opens at its contact 6 the energizing circuit for starting contactor ST. The closing of contact 8 of relay 2AP completes, through contact 9 of relay (TR, a circuit for supplying current from alternator I2 over leads 2T! and 2T2 to warm-up timer 2WUT causing its motor M to run and its clutch to engage to drive the earns 31 and 38. When relay 2WUT has operated for about four and onequarter minutes, its contact 8 closes to prepare a partial energizing circuit for relay ZTSC comprising lead 2Tl, contact 9 of relay ITR, windof relay 2TSC, resistor 39, condenser 40, open contact I of hold-over timer IHOT, contact 8 of timer ZWUT to lead 2T2, this circuit being completed when contact I of timer IHOT closes, as will be described below.

When power failure relay ZPF operates, it completes a circuit from lead 2T! to hold-over timer IHOT, contact it of relay 2TB, contact of relay 2PF and contact 9 of relay ICL to lead 2T2 to cause the operation of timer IHOT. The clutch of the timer engages and its motor In drives the cams 4| and 82. The hold-over timer has a four and three-quarter minute control, contact 8 operated by cam 4|, set to prevent stopping of engine II in case the operation of engine-alternator l2, I3 is not satisfactory to assume the load. It also has a four and one-half minute control, contact operated by cam 42, to permit transferring the load from alternator ID to alternator l2.

The closing of contact I of timer IHOT completes a circuit from lead 2T2 through contact 8 of timer ZWUT, contact 1 of IHOT, condenser 40, resistor 39, winding of relay ZTSC, contact 9 of relay I'I'H to lead lTl, causing relay ZTSC to operate. A circuit is thus completed from lead ZTI through contact 9 of relay ITR, contact of relay ZTSC, armature A of transfer switch TS, the winding of TS, armature 3 of TS to lead 2T2. The transfer switch TS is thus operated to transfer the load from alternator 10 to alternator 12.

When contact 8 of timer ll-IOT closes, a circuit is completed from lead 2T2 through contact 9 of relay ICL, contact of relay ZPF, contact 8 of timer IHOT, winding of relay ZTR to lead 2Tl, thereby operating transfer relay 2TB. Relay 2TB. locks up through its contact 3 and the contact of relay ZPF. The energizing circuit for timer IHOT is opened at contact In of relay ZTR to release timer IHOT. The opening of contact 9 of relay 2TB opens the circuit through the contact of relay ITSC going to a contact and armature 4 of transfer switch TS, thus leaving switch TS ready to be operated to transfer the load from alternator l2 to alternator [0 at the end of the twelve hour period of operation of alternator 12, or in the event that alternator 1! falls during the twelve hour operating period. The opening of contact H of relay 2TB opens the energizing circuit, for main control relay IMC to cause it to release.

Release of relay IMC opens the circuit from negative battery through contact I of relay IMC, lead Pl, winding of relay PI of apparatus 14 to ground, causing relay Pl to release. A circuit is thus completed from negative battery through lead B, contact of relay Pl, contact 6 of relay ASD! and air shut-down valve ASD to ground, thereby operating the air shut-down valve ASD to stop engine I l. The energizing circuit for pilot I relay IP is opened at contact 3 of relay IMC and at contact ll of relay ZTR. Release of relay IP opens at its contact 3 the energizing circuit for relay ASDI of apparatus M. The circuit for operating start relay ST of apparatus 14 is opened at contacts 2 of relay IP. The ASDT time operates to release ASDl and after it cools, the circuit is then restored to normal with engine alternator [0, ll ready to take over the load at the end of a twelve hour operating period of enginealternator I2, [3 or if the engine alternator I2, l3

I should fail for any reason.

The operation of restarting the engine-alternator H), H and the transfer of the load from alternator l2 to alternator I0 is similar to that '6 described above for starting engine l3 and for transferring the load from alternator [0 to alternator l2. Stated briefly, when contact 4 of cycle timer CT closes, relay ICL is energized to cause its operation and to cause relay 2CL to release relays ZPF and 2TB. Relays IMC and [P are operated to cause the operation of relay PI and start relay ST of apparatus [4. The engine II is thus started to cause it to drive alternator l0 and when its voltage builds up, relays IAP and IPF operate. Warm-up timer IWUT and holdover timer 2HOT are energized and relay ITSC is operated. A resistor 10 and a condenser II are provided in circuit with the winding of relay ITSC as are the resistor 39 and condenser 40 in circuit with the winding of relay ZTSC to prevent relay operation if both frequency and Voltage are not correct. The transfer relay TS is energized to transfer the load from alternator [2 to alternator Hi.

When either engine-alternator I0, I l or enginealternator l2, I3, while carrying the load,' is shut down due to low oil pressure, high water temperature or over speeding, as will be described below, the associated power failure relay PF, the cycle-timer relay CL and the warm-up timer short-circuiting relay WUTS are released. Assuma'for example, that engine-alternator H], II is carrying the load and that it is shut down due to one of the above causes, power failure relay IPF, cycle-timer relay ICL and warm-up timer short circuiting relay WUTS are released. When relay IPF releases, its contact opens to cause transfer relay ITR to release. Contact ll of relay ITR closes to cause relay ZMC to operate and the operation of relay ZMC completes a circuit causing relay 2P to operate. The engine 13 is thus caused to start as previously described. Then power failure relay ZPF and alternator potential relay ZAP are operated, as described above. As soon as the output voltage of alternator I2 builds up to the required voltage, warm-up timer 2WUT start to operate and at the end of a period of fifteen to twenty-five seconds, the transfer switch control relay ZTSC is operated because of the completion of an energizing circuit from lead 2T2, through contact I of timer ZWUT, contact 6 of relay WUTS, condenser 40, resistor 39, winding of relay ZTSC and contact 9 of relay lTR to lead ZTI. When relay ZTSC operates, its contact closes to complete a circuit for supplying current from alternator l2 to. transfer switch TS, causing it to operate and transfer the load to alternator l2. Alternator I 2 will then carry the load unti1 the trouble condition on engine-alternator l0, H has been corrected.

k If'the engine lubricating oil pressure drops too low or if the engine cooling liquid temperature becomes too high, the engine H or I3 is stopped automatically. When the lubricating oil pressure for engine I I, for example, rises to 10 pounds per square inch, the contacts of the low oil pressure switch LOPS open. When the fuel oil pressure rises to 6 pounds per square inch, the contacts of fuel oil pressure switch FPS close. The opening of contacts LOPS and the closing of con tacts FPS prepare the protective circuits to shut the engine down in case LOPS closes because lubricating oil pressure drops below 10 pounds per square inch, or in case high water temperature switch HWTS closes because the cooling liquid temperature reaches a certain abnormally high value. To prevent false operation of the low oil pressure switch shutdown during the starting period, if the fuel oil pressure should build up sufficiently to close the fuel oil pressure switch contacts before the contacts of LOPS open, the oil pressure delay thermal relay 'OPD is provided. It the fuel oil pressure switch FPS contacts and the contacts of LOPS are closed at the same time or a period of twenty to thirty-five seconds, the CPD heater closes the CPD contacts and relay LOP is operated. When relay LCP operates, or when the contacts of HWTS close, a circuit is completed from negative battery through the contacts of HWTS or through the contacts of relay LOP, lead LOHW and winding of relay ILOHW to ground, thereby causing relay ILOHW to operate and to look up through its contact 3. Contact 5 of relay ILOHW opens to release relay IMC to cause the engine 1] to stop. Engine 13 will then be started as described above, and cur rent will be supplied to the load from alternator i2. The cycle timer will continue to operate and contact 4 will subsequently close. Relay IOL will operate and relay MIL will release. When contact 9 of ICL opens, power failure relay ZPF releases and transfer relay 2TH. releases. Contact l i of ZTR closes but main control relay [MC cannot operate to start engine H because contact 5 of relay lLOl-IW is open. Therefore, engine H cannot be started and the load will continue to be supplied from alternator I2.

It the startng motor current is excessive such as would occur if the engine bearings seize, thermal relay OL'I' operates to open the energizing circuit for relay IMC or 2M0, causing relay IP or 2P'to release to open the starting circuit by opening contacts 2 of the IP or 2P relay and the motor M of apparatus [4 or apparatus [5 cannot crank the engine H or the engine 13 until therelay LT is reset manually. The alternator which is carrying the load will continue to do so.

When relay iP operates to complete a circuit for operating the starting relay -ST of apparatus [4, for example, a circuit is also closed from negative battery through contact 4 of over-cranking relay 10C, contacts 2 of relay lP, contact 6 of relay lAP, lead C04, contacts of relay CCO, contacts of switch ESW, lead CO and the heater of thermal switch I CRT to ground, thereby operating relay ICRT to cause it to close its contacts after a delay period of about thirty-five seconds if the engine has not started in that time. lay iOC is thus energized to cause it to open at its contact 4 the ener izing circuit for starting contactor ST and, at its contact 8 the energizing circuit for relay lMC. Subsequently, the engine cannot be cranked until the relay iCRT is reset by hand.

When the engine speed reaches 1360 to 1430 revolutions per minute, the over-speed trip switch OSTcloses its contacts to complete an energizing circuit for causing the operation of relay OSTI of apparatus 14, for example. A circuit is thus completed from negative battery through contact of relay OSTl, lead 0ST, winding of overspeed trip relay IOST, lead PX2 and relay 0LT to ground, thereby causing relay IOST to operate and lock up through its contact 4. Closing of contact 5 of relay IOST completes an energizing circuit for relay IOS. Contact 6 oi. relay [OS is closed to energize an alarm circuit 53'. Contact 4 of relay IOS opens to interrupt the enersizing circuit for relay IMC, thereby stopping the engine ii. To subsequently start engine H it is necessary to manually reset the relay IOST. Ii any of the battery fuses of apparatus H or 15,

or if either of the discharge fuses 35 blows, an

8 energizing circuit is completed for operating the IOST or the ZOST relay to stop the engine H 0! l3, respectively.

There are provided a motor 58 for operating air recirculating louver for engine H and a motor 50 for operating air recirculating louver for ensine H, the circuits for energizing motors 58 and 50 being completed by controllers 59 and GI, respectively. Whether these louvers are open or shut depends upon the position of the controller which, in turn, depends upon the room temperature. When the controller 59 is in a positionv to complete an energizing circuit for motor 58. current is supplied from alternator Hi to a circuit comprising lead Tl, lead Ll, fuse 55, lead 5|, controller 59, motor 58, lead 50, fuse 54, line L2 and line T2. Similarly, when the controller BI is in a position to complete an energizing circuit for motor 60, current is supplied from alternator 12 to a circuit comprising lead 2Tl, lead Ll, ruse 51, lead 53, motor 60, controller 5|, lead 52, fuse 55, line L2 and line 2T2.

If fuse 54 or 56 should blow, relay IF'AI is released. If relay IFA is operated, the release of relay IFAI completes a circuit from ground through a contact of relay IFA, winding of thermal relay IFAD, resistor 62 to negative battery. After a delay period of 1.5 to 2.5 minutes, relay IFAD operates to complete a circuit for energizing relay IOST. Operation of relay IOST oompletes a circuit for causing relay IOS to operate, thereby completing a circuit for energizing the alarm 53. If relay IFA should be released, however, due to no voltage across line Li, L2 going to the load, the relay IFAD will not be energized and the alarm 53 will not be energized. Similarly, if fuse 55 or '51 should blow a circuit is 001m pleted for energizing the alarm 63, relay ZFAD being energized through a circuit comprising a resistor 63, heater or ZFAD and contacts of relays ZFA and ZFAI.

In the event that neither alternator l0 nor alternator I2 is running so that no output voltage is produced across leads Ti, T2 and no output voltage is produced. across leads ZTI and 2T2,

relay iFA2 and relay 2FA2 will both be released since the winding of relay IFAZ is connected across leads TI and T2 and the winding of relay iFAZ is connected across leads 2'1! and 2T2. In this case an energizing circuit for relay IFAD is completed through contact 5 of relay ZFAI. and contact 4 of relay IFA2, and an energizing circuit for relay 2FAD is completed through contact 6 of relaly iFAz and contact A of relay 2FA2; Relays IFAD and ZFAD will, therefore, operate to cause the energization of the alarm circuit 63; In this case an alarm 64 will also be energized under control of relay ZFA. Relay ZFA will release due to no voltage across the load line Ll, L2 to cause it to close its contact 4, thereby connecting ground to alarm circuit 64 to complete an energizing circuit from negative battery for the alarm circuit 54.

This application discloses but does not claim subject-matter that is disclosed and claimed in our application Serial No. 304,316, filed August 14, 1952.

What is claimed is:

1. In a power supply system, a source of electrical power, a first relay having a Winding connected across said first source and a pair of make contacts, a load device, a second relay'having a winding connected across said load device and a pair of break contacts, circuit interrupting means connecting said load device to said first 9 power source, a second source of electrical power, a third relay having a winding connected in series with the contacts of said first and second relays across said second source of power and supervisory means controlled by said third relay, whereby d t ird relay is operated when said first means functions to interrupt the connection between the first source and the load device but is not operated when the power from said first source fails.

2. In combination, a first, a second and a third relay each having a winding, one of said first and second relays having a pair of contacts which are open when the relay is not energized, the other of said first and second relays having a pair of contacts which are closed when the relay is not energized, a first current source, a load current path comprising a load, circuit interrupting means connecting said load current path to said first current source, means for connecting the winding of said first relay across said first current source, means for connecting the winding of said second relay across said load current path, a second current source and means comprising the contacts of said first relay and the contacts of said second relay for connecting the winding of said third relay to said second current source.

3. A combination in accordance with claim 2 in which there are provided an alarm circuit and means responsive to the energization of said third relay for controlling the energization of said alarm circuit.

4. In combination, a first, a second and a third relay each having a Winding, said first relay having a first pair of contacts which are closed when the relay is energized and a second pair of contacts which are open when the relay is energized, said second relay having a pair of contacts which are open when said relay is energized, said third relay having a pair of contacts which are closed when said relay is energized, a first current source, a load current path comprising a load, circuit interrupting means connecting said load current path to said first current source, means for connecting the winding of said first relay across said first current source, means for connecting the winding of said second relay across said load current path, a second current source, means comprising said first pair of contacts of said first relay and the contacts of said second relay for connecting the winding of said third relay to said second current source, a first alarm circuit, means responsive to the closing of said second pair of contacts of said first relay for connecting said first alarm circuit to said second current source, a second alarm circuit and means responsive to the energization of said third relay for controlling the energization of said second alarm circuit.

5. In combination, a first and a second current supply source for alternately supplying current to a common load, a third current source, a first, a second, a third, a fourth and a fifth relay each having a winding, one of said first and second relays having a pair of contacts which are closed when said relay is energized, the other said first and second relays having a pair of contacts which are open when said relay is energized, a current path comprising an auxiliary load, means including circuit interrupting means for connecting said current path to said first current source, means for connecting the winding of said first relay across said first current source, means for connecting the winding of said second relay across said current path, means comprising the contacts of said first and second relays for connecting the winding of said third relay to said third current source, an alarm circuit, means responsive to the energization of said third relay for controlling the energization of said alarm circuit, said fourth and fifth relays each having a pair of contacts which are open when the relay is energized, means for connecting the winding of said fourth relay across said first current source, means for connecting the winding of said fifth relay across said second current source and means comprising the contacts of said fourth and fifth relays for connecting the winding of said third relay to said third current source.

VINCENT T. CALLAHAN.

LLOYD D. FRY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 524,636 Jaeger l- 579,556 Badt Mar. 30, 1897 1,720,738 Boutillier July 16, 1929 1,761,002 Williams June 3, 1930 1,800,394 Lunsford Apr. 14, 1931 

